The present invention relates to a process for controlling a drilling operation.
During the drilling of an oil well, the motor of the drill-rod string, which is mounted on the surface, rotates at a constant speed of approximately 50 to 150 revolutions per minute. However, the friction generated between the drilling tool and the bottom of the well or between the rods and the wall of the well can cause slowdowns and indeed even periodic stops of the tool. Since the motor continues to rotate at one end of the drill-rod string during this time, the latter tends to twist about its longitudinal axis, until the force exerted is greater than the frictional effect braking the tool. At this moment, the drill-rod string is relieved and the tool begins to rotate again at speeds which can reach peak rotational speeds of the order of 150 to 400 revolutions per minute. Since wells often follow broken paths, contact between the casing and the wall of the well occurs somewhat frequently.
It is clear that the behaviour of the tool has an important effect on the progress of the drilling operation. It is therefore desirable that the foreman driller be warned of periodic instabilities in the rotational speed of the tool, so that he can modify the drilling parameters, namely the rotational speed of the motor, the weight exerted on the tool and the mud flow rate, and thus ensure optimum drilling.